Well treatment fluids composition

ABSTRACT

A well treatment fluid composition that includes a tetrakis(hydroxyorgano)phosphonium salt and 1,3-dimethylol-5,5-dimethylhydantoin. Methods for preparing a well treatment fluid composition and treating a subterranean formation are also presented.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit of priority under 35 U.S.C. §119(e) of U.S. Provisional Application Ser. No. 62/263,836, filed onDec. 7, 2015, the entire disclosure of which is incorporated herein byreference.

BACKGROUND

Microorganisms in oilfields or in injection water where water iscollected from ponds or similar water sources may include iron-oxidizingbacteria, sulfate-reducing bacteria, slime-forming bacteria, sulfideoxidizing bacteria, yeast and molds, and protozoa. Biocides are used totreat water and destroy bacteria or a substantial amount of bacteriaduring a biocide treatment.

There is constant demand for new treatment fluids biocides to controlthe proliferation of undesired bacteria in oil and gas applications,notably in hydraulic fracturing and oil field reservoir treatments tocontrol reservoir souring.

SUMMARY

The present invention provides a more effective, cost-efficient,sustainable well treatment biocide composition with impact upon theexternal environment minimized.

The present disclosure provides a composition suitable in or as a welltreatment composition that includes a tetrakis(hydroxyorgano)phosphoniumsalt, herein-referred as “THP salt”, and1,3-dimethylol-5,5-dimethylhydantoin.

The 1,3-dimethylol-5,5-dimethylhydantoin of the invention has typicallythe following formula:

It was found that the composition of the present invention provided afast kill whilst pumping. It was also found that the composition of theinvention provided long term preservation after pumping and enhancedbiofilm control to prevent or mitigate reservoir souring. In certainembodiments, the composition of the present invention allows to achieveboth effects as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides a standard quantitative suspension test on the effect ofthe composition based on THPS and 1,3-Dimethylol-5,5-dimethylhydantoin(referred to as DANTOGARD® 2000 and treatment concentrations expressedas product containing approximately 50% active ingredient of1,3-Dimethylol-5,5-dimethylhydantoin) against General HeterotrophicBacteria Pseudomonas aeruginosa contained in an artificial biofilm;

FIG. 2 provides a standard quantitative suspension test on the effect ofthe composition based on THPS and 1,3-Dimethylol-5,5-dimethylhydantoin(referred to as DANTOGARD® 2000 and treatment concentrations expressedas product containing approximately 50% active ingredient of1,3-Dimethylol-5,5-dimethylhydantoin) against General HeterotrophicBacteria Pseudomonas aeruginosa contained in an artificial biofilm;

FIG. 3 provides a standard quantitative suspension test on the effect ofthe composition based on formulated THPS and1,3-Dimethylol-5,5-dimethylhydantoin (referred to as DANTOGARD® 2000 andtreatment concentrations expressed as product containing approximately50% active ingredient of 1,3-Dimethylol-5,5-dimethylhydantoin) againstGeneral Heterotrophic Bacteria Pseudomonas aeruginosa contained in anartificial biofilm;

FIG. 4 provides a standard quantitative suspension test on the effect ofthe composition based on THPS and 1,3-Dimethylol-5,5-dimethylhydantoinagainst planktonic sulphate reducing bacteria;

FIG. 5 provides a standard quantitative suspension test on the effect ofthe composition based on THPS and 1,3-Dimethylol-5,5-dimethylhydantoin(referred to as DANTOGARD® 2000 and treatment concentrations expressedas product containing approximately 50% active ingredient of1,3-Dimethylol-5,5-dimethylhydantoin) against planktonic GeneralHeterotrophic Bacteria Pseudomonas aeruginosa; and

FIG. 6 provides a standard quantitative suspension test on the effect ofthe composition based on THPS and 1,3-Dimethylol-5,5-dimethylhydantoin(referred to as DANTOGARD® 2000 and treatment concentrations expressedas product containing approximately 50% active ingredient of1,3-Dimethylol-5,5-dimethylhydantoin) against Lactobacillus Brevis.

DETAILED DESCRIPTION

In general, well treatment compositions according to the presentdisclosure include a THP salt and 1,3-dimethylol-5,5-dimethylhydantoin.Experimental results surprisingly indicate that a simultaneous use of aTHP salt and 1,3-dimethylol-5,5-dimethylhydantoin in well treatmentfluids lead to a particularly effective treatment.

While specific embodiments are discussed, the specification isillustrative only and not restrictive. Many variations of thisdisclosure will become apparent to those skilled in the art upon reviewof this specification.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as is commonly understood by one of skill in theart to which this specification pertains.

As used in the specification and claims, the singular form “a”, “an” and“the” includes plural references unless the context clearly dictatesotherwise.

As used herein, and unless otherwise indicated, the term “about” or“approximately” means an acceptable error for a particular value asdetermined by one of ordinary skill in the art, which depends in part onhow the value is measured or determined. In certain embodiments, theterm “about” or “approximately” means within 1, 2, 3, or 4 standarddeviations. In certain embodiments, the term “about” or “approximately”means within 50%, 20%, 15%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%,0.5%, or 0.05% of a given value or range.

Also, it should be understood that any numerical range recited herein isintended to include all sub-ranges subsumed therein. For example, arange of “1 to 10” is intended to include all sub-ranges between andincluding the recited minimum value of 1 and the recited maximum valueof 10; that is, having a minimum value equal to or greater than 1 and amaximum value of equal to or less than 10. Because the disclosednumerical ranges are continuous, they include every value between theminimum and maximum values. Unless expressly indicated otherwise, thevarious numerical ranges specified in this application areapproximations.

The present disclosure also provides a method of treating a water systemcontaminated, or liable to contamination, with microbes such asbacteria, fungi or algae, which method includes adding to the systemseparately or together, a biocidally active amount of a THP salt and1,3-dimethylol-5,5-dimethylhydantoin.

The water system may, for instance, be contaminated with bacterial slimeand/or planktonic bacteria. Compositions of the present disclosure maybe of use for treating aerobic systems such as cooling towers, paperprocessing systems and waste water systems, and also for anaerobicsystems, such as oil wells, e.g. during secondary recovery. Compositionsof the present disclosure may also be suitable for use in thepreservation of slurries and functional fluids, such as drilling muds,completion fluids, stimulation fluids and fracturing fluids.

In the present invention the active microbes may be active bacteria(e.g. general heterotrophic bacteria (GHB), sulphate-reducing bacteria),or other active microbes, such as archaea, (e.g. methanogenic archaea orsulphate-reducing archaea). Thus the microbial activity may be due toactive bacteria or to other active microbes, such as archaea.

The invention may be used in relation to any bacteria (or othermicrobes) that can be found in petroleum reservoirs, includingsulphate-reducing prokaryotes (SRP) (which may be sulphate-reducingbacteria and/or sulphate-reducing archaea), general heterotrophicbacteria (GHB), and nitrate-reducing bacteria (NRB).

As used herein, the term “well treatment fluid” is meant to encompasspartial and/or complete compositions suitable for introduction into awellbore or subterranean formation. Well treatment fluids include, butare not limited to, hydraulic fracturing fluids.

According to one specific feature, the compositions of the inventionfurther comprise at least one oxidizing viscosity breaker.

In certain embodiments, the well treatment fluid includes the oxidizingviscosity breaker in an amount from about 15 ppm to about 250 ppm activeingredient (e.g. breaker).

In certain embodiments, the well treatment fluid includes the THP saltin an amount from about 40 ppm to about 250 ppm active ingredient.According to an interesting embodiment, the THP salt istetrakis(hydroxymethyl)phosphonium sulphate, herein-referred as “THPS”.Other THP salts include the phosphite, bromide, fluoride, chloride,phosphate, carbonate, acetate, formate, citrate, borate, and silicate.

In certain embodiments, the well treatment fluid includes a THP salt,1,3-dimethylol-5,5-dimethylhydantoin, a quaternary ammonium compound,and an oxidizing viscosity breaker. In a particular embodiment, thequaternary ammonium compound is benzalkonium chloride. In certainembodiments, the quaternary ammonium compound is present in an amountfrom about 5 ppm to about 50 ppm.

In certain embodiments, the well treatment fluid includes a THP salt,1,3-dimethylol-5,5-dimethylhydantoin, a polymer of an unsaturatedcarboxylic acid or a copolymer of an unsaturated carboxylic acid with asulphonic acid, the polymer or copolymer being terminated by a mono- ordi-phosphonated unsaturated carboxylic add group or having such monomersincorporated into the polymer backbone. In certain embodiments, thepolymer or copolymer is either terminated by vinylphosphonic acid (VPA)or vinylidene-1,1-diphosphonic acid (VDPA) or has such monomersincorporated into the polymer backbone; accordingly the polymer may be arandom copolymer incorporating VPA and/or VDPA monomers.

In other embodiments, the polymer is a polyacrylate or anacrylate/sulphonate copolymer. In certain embodiments, the polymer is apolyacrylate terminated with vinylphosphonic acid, (hereinafter “VPAend-capped polymer”) or with vinylidene-1,1-diphosphonic acid(hereinafter “VDPA end-capped polymer”), or is a polyacrylateincorporating VPA and/or VDPA monomers. In other embodiments, thepolymer is an acrylate/sulphonate copolymer terminated withvinylidene-1,1-diphosphonic acid (hereinafter “VDPA end-cappedcopolymer”) or with vinylphosphonic acid (hereinafter “VPA end-cappedco-polymer”), or is an acrylate/sulphonate copolymer incorporating VPAand/or VDPA monomers.

In certain embodiments, the ratio of VPA or VDPA end-capped polymer orcopolymer to THP salt, is, when expressed as a percentage by weight, inthe range of from 0.5 to 50%, such as from 0.5 to 30%; preferably from 1to 25%, such as from 1 to 20%, for example from 1 to 10% or from 2 to8%; most preferably from 1 to 5%, for example from 3 to 5% (based uponactive solids and upon a 1 to 74%, for example a 50%, active THP saltformulation).

In certain embodiments, it may be used a combination of the THP salt andthe polymer of an unsaturated carboxylic acid or a copolymer of anunsaturated carboxylic acid with a sulphonic acid as disclosed in WO2005/074688.

In certain embodiments, the oxidizing viscosity breaker is selected fromperoxides (e.g. hydrogen peroxide), persulfates (e.g. sodium persulfate(“SP”), encapsulated ammonium persulfate (“AP”)), and chlorites (e.g.sodium chlorite (“SC”)).

In certain embodiments, the oxidizing viscosity breaker is present inthe well treatment fluid in an amount that is effective to reduce theviscosity of the fluid. In certain embodiments, the breaker is presentin an amount of at least about 0.25 gallons of dilute solutioncontaining the breaker per thousand gallons of well treatment fluid(gpt), in some cases at least about 0.5 gpt, and can be up to about 1.5gpt, in some cases up to about 3.0 gpt. In other embodiments, thebreaker is present in an amount of at least about 0.25 pounds of dilutesolution containing the breaker per thousand gallons of well treatmentfluid (ppt), in some cases at least about 0.5 ppt, and can be up toabout 2.0 ppt, in some cases up to about 3.0 ppt. The amount of dilutesolution containing a breaker used in the friction reducing treatmentsolution can be any value or range between any of the values recitedabove. In certain embodiments, the dilute solution contains from about 5wt % to about 10 wt % breaker in water.

As used herein, the term “dilute solution” means a solution containing alow concentration of solute compared to solvent. In certain embodiments,“solute” refers to breaker, biocide, or other active ingredient. Incertain embodiments, the solvent is aqueous and includes water.

The THP salt and 1,3-dimethylol-5,5-dimethylhydantoin are present in thewell treatment fluid in amounts that are effective to control or reducea microbial population in the fluid. In an embodiment, compositions ofTHPS and 1,3-dimethylol-5,5-dimethylhydantoin contain less than 0.2%free formaldehyde after 4 months storage at 50° C., which is quitesurprising for compositions containing a formaldehyde-release agent. Theexact content of the composition of the present invention has to bedefined on a case by case basis, but typically:

-   -   the THP salt is present in an amount of at least about 0.1        gallons of THP salt per thousand gallons of well treatment fluid        (gpt) and, preferably at least about 0.25 gpt; the THP salt can        be up to about 3 gpt, notably up to about 1.5 gpt, for example        up to about 0.75 gpt.    -   the 1,3-dimethylol-5,5-dimethylhydantoin is typically present in        an amount of about 0.1 to 15 gpt, notably about 1 to 10 gpt.    -   the mass ratio between the THP salt and        1,3-dimethylol-5,5-dimethylhydantoin in a composition is about        1:0.5 to 1:25, preferably about 1:2.5 to 1:12.5, for example        about 1:0.6, 1:1.25, 1:1.8, 1:5 or 1:10.

In other embodiments, a THP salt, and1,3-dimethylol-5,5-dimethylhydantoin and a quaternary ammonium compound(“quat”) are present in the well treatment fluid. In certainembodiments, the THP salt/quat combination is present in an amount of atleast about 0.1 gallons of THP salt/quat per thousand gallons of welltreatment fluid (gpt) and can be up to about 0.3 gpt. These ranges forgpt correspond to a range from about 50 ppm to about 150 ppm biocide.The amount of THP salt or THP salt/quat used in the friction reducingtreatment solution can be any value or range between any of the valuesrecited above. In certain embodiments, the dilute solution contains fromabout 15 wt % to about 55 wt % THP salt in water. In certainembodiments, the dilute solution contains from about 45 wt % to about 55wt % THP salt and quat in water.

In certain embodiments, a method for preparing a well treatment fluidcomposition is provided. In a particular embodiment, the method includesthe steps of obtaining a well treatment composition that includes a THPsalt and 1,3-dimethylol-5,5-dimethylhydantoin; and diluting thecomposition to form a diluted composition. In certain embodiments, thewell treatment composition further at least one oxidizing viscositybreaker. In certain embodiments, the well treatment composition furtherincludes a quaternary ammonium compound.

Also provided are methods for treating a subterranean formation thatinclude the step of introducing a well treatment composition thatincludes:

-   -   a THP salt,    -   1,3-dimethylol-5,5-dimethylhydantoin,    -   optionally at least one oxidizing viscosity breaker,    -   optionally a polymer of an unsaturated carboxylic acid,    -   optionally a copolymer of an unsaturated carboxylic acid with a        sulphonic acid, and    -   optionally a quaternary ammonium compound.

The present invention will further illustrated by the followingexamples. The examples given herewith are not intended to be limiting.Unless otherwise indicated, all percentages are by weight of the totalcomposition.

EXAMPLES

As used herein, the abbreviation “ai” refers to active ingredient.

Example 1—Composition Based on THPS and1,3-Dimethylol-5,5-Dimethylhydantoin, Such as DANTOGARD® 2000 (Lonza),Against General Heterotrophic Bacteria Pseudomonas aeruginosa Containedin an Artificial Biofilm

Sample Preparation.

250 ppm 1,3-Dimethylol-5,5-dimethylhydantoin and 50 ppm THPS were usedto treat an artificial biofilm containing General Heterotrophic BacteriaPseudomonas aeruginosa. A sterile QST medium was used for the studies.The bacterial challenge comes from the artificial biofilm. Studs wereprepared from a 16 hour Pseudomonas aeruginosa culture grown in theappropriate growth medium. A sterile filter paper (Whatman No. 2) wasplaced onto an agar plate. 1 ml of 16 hr old culture was placed onto thesurface and spread over the filter paper using a sterile spreader. Usingsterile forceps 5 sterile freeze drying rubber bungs with O rings wasplaced onto the filter paper. The plates were incubated at 30° C. forapproximately 5 days until the plate was covered with growth. The studswith biofilm were exposed to the biocide treatment for various contacttimes from 0 to 336 hours.

Sample Analysis.

The efficiency of the biocide treatments is measured using a standardquantitative suspension test (QST) method and enumerated using a mostprobable number (MPN) method. The efficiency of the biocide treatmentswas measured using a standard quantitative suspension test (QST) methodand enumerated using a most probable number (MPN) method. A typical QSTprocedure is described as follows: 90 ml of QST medium is dispensed intoglass screw cap bottles (100 ml nominal capacity) with magneticfollowers and cap with the modified tops. The bottles and contents weresterilised by autoclaving (121° C. for 15 minutes). On cooling a further9 ml of sterile QST medium was added to the bottles to bring the finalvolume to 99 ml. Immediately prior to the test the biocide stocksolutions (1,3-Dimethylol-5,5-dimethylhydantoin and THPS) were preparedin sterile QST medium at a concentration such that when 1.0 ml was addedto the test bottles the desired concentration was achieved (final testvolume 100 ml). They were added to the test samples immediatelyfollowing preparation The bottles were placed on a Multiplate magneticstirrer to mix the biocide. The stock solutions were prepared atconcentrations on a weight for volume basis mg/ml such that when 1.0 mlwas added to the inoculated QST medium (final volume 100 ml) the desiredfinal concentration of biocide was achieved. Two bottles were set up perbiocide being tested per time point and two bottles for a biocide freecontrol. Using sterile forceps one stud was removed from the plate,taking care not to disturb the biofilm, and using the modified topsplace in the test bottles. Approximately 2 ml amounts of sterile glassbeads of 1.5 to 2.5 mm diameter and sterile acid washed sand 50-150 meshwas dispensed into sterile screw cap plastic universal containers (30 mlnominal capacity). To these was added 10 ml sterile neutralisingsolution, QST medium supplemented with 5 g/L Sodium Thiosulphate and 5g/L Glycine. One container is required per stud. A further two studs areremoved from the plates for the Time 0 control samples and placeddirectly into the neutralising medium. The contents were vortex mixed atmaximum speed in 3 consecutive 45 second bursts with a 15 secondinterval between each burst. The purpose of this procedure is tomechanically remove biofilm from the surface of the coupons and tofurther disrupt the removed biofilm into small fragments therebyproducing a reasonably uniform dispersion of biofilm for enumeration. Analiquot of 5 ml was removed from each bottle and pooled into a thirdbottle and mixed thoroughly. 1.0 ml aliquots were removed from thepooled dispersion mix and inoculated into the first tube of a dilutionseries. This was carried out in duplicate. A serial dilution (10 foldsteps) was carried out in the appropriate growth medium. At thepredetermined time points the studs were removed from the test samplesand place in the neutralising medium. The studs were processed in thesame way as for the control sample. 1 ml aliquots were inoculated forthe pooled samples in the first tube of a dilution series. This wascarried out in duplicate. A serial dilution (10 fold steps) was carriedout in the appropriate growth medium, with the first tube in each seriescontaining the same medium supplemented with glycine (5.0 g/l) andsodium thiosulphate (5.0 g/l) to inactivate any residual biocide carriedinto the dilution series with the QST medium. The dilution series wasincubated at 25° C. and read after 48 hours. The end point was scored asthe highest dilution in the series to show turbidity.

The experiment shows that at all contact times the combination of THPSand and 1,3-Dimethylol-5,5-dimethylhydantoin provide an enhancedreduction in bacterial numbers. (FIG. 1).

Example 2—Composition Based on THPS and1,3-Dimethylol-5,5-Dimethylhydantoin, Such as DANTOGARD® 2000 (Lonza),Against General Heterotrophic Bacteria Pseudomonas aeruginosa Containedin an Artificial Biofilm

Sample Preparation.

500 ppm 1,3-Dimethylol-5,5-dimethylhydantoin and 50 ppm THPS were usedto treat an artificial biofilm containing General Heterotrophic BacteriaPseudomonas aeruginosa. A sterile QST medium was used for the studies.The bacterial challenge comes from the artificial biofilm. Studs wereprepared from a 16 hour Pseudomonas aeruginosa culture grown in theappropriate growth medium. A sterile filter paper (Whatman No. 2) wasplaced onto an agar plate. 1 ml of 16 hr old culture was placed onto thesurface and spread over the filter paper using a sterile spreader. Usingsterile forceps 5 sterile freeze drying rubber bungs with O rings wasplaced onto the filter paper. The plates were incubated at 30° C. forapproximately 5 days until the plate was covered with growth. The studswith biofilm were exposed to the biocide treatment for various contacttimes from 0 to 336 hours.

Sample Analysis.

The efficiency of the biocide treatments is measured using a standardquantitative suspension test (QST) method and enumerated using a mostprobable number (MPN) method. The efficiency of the biocide treatmentswas measured using a standard quantitative suspension test (QST) methodand enumerated using a most probable number (MPN) method. A typical QSTprocedure is described as follows: 90 ml of QST medium is dispensed intoglass screw cap bottles (100 ml nominal capacity) with magneticfollowers and cap with the modified tops. The bottles and contents weresterilised by autoclaving (121° C. for 15 minutes). On cooling a further9 ml of sterile QST medium was added to the bottles to bring the finalvolume to 99 ml. Immediately prior to the test the biocide stocksolutions (1,3-Dimethylol-5,5-dimethylhydantoin and THPS) were preparedin sterile QST medium at a concentration such that when 1.0 ml was addedto the test bottles the desired concentration was achieved (final testvolume 100 ml). They were added to the test samples immediatelyfollowing preparation. The bottles were placed on a Multiplate magneticstirrer to mix the biocide. The stock solutions were prepared atconcentrations on a weight for volume basis mg/ml such that when 1.0 mlwas added to the inoculated QST medium (final volume 100 ml) the desiredfinal concentration of biocide was achieved. Two bottles were set up perbiocide being tested per time point and two bottles for a biocide freecontrol. Using sterile forceps one stud was removed from the plate,taking care not to disturb the biofilm, and using the modified topsplace in the test bottles. Approximately 2 ml amounts of sterile glassbeads of 1.5 to 2.5 mm diameter and sterile acid washed sand 50-150 meshwas dispensed into sterile screw cap plastic universal containers (30 mlnominal capacity). To these was added 10 ml sterile neutralisingsolution, QST medium supplemented with 5 g/L Sodium Thiosulphate and 5g/L Glycine. One container is required per stud. A further two studs areremoved from the plates for the Time 0 control samples and placeddirectly into the neutralising medium. The contents were vortex mixed atmaximum speed in 3 consecutive 45 second bursts with a 15 secondinterval between each burst. The purpose of this procedure is tomechanically remove biofilm from the surface of the coupons and tofurther disrupt the removed biofilm into small fragments therebyproducing a reasonably uniform dispersion of biofilm for enumeration. Analiquot of 5 ml was removed from each bottle and pooled into a thirdbottle and mixed thoroughly. 1.0 ml aliquots were removed from thepooled dispersion mix and inoculated into the first tube of a dilutionseries. This was carried out in duplicate. A serial dilution (10 foldsteps) was carried out in the appropriate growth medium. At thepredetermined time points the studs were removed from the test samplesand place in the neutralising medium. The studs were processed in thesame way as for the control sample. 1 ml aliquots were inoculated forthe pooled samples in the first tube of a dilution series. This wascarried out in duplicate. A serial dilution (10 fold steps) was carriedout in the appropriate growth medium, with the first tube in each seriescontaining the same medium supplemented with glycine (5.0 g/l) andsodium thiosulphate (5.0 g/l) to inactivate any residual biocide carriedinto the dilution series with the QST medium. The dilution series wasincubated at 25° C. and read after 48 hours. The end point was scored asthe highest dilution in the series to show turbidity.

The experiment shows that at all contact times the combination of THPSand and 1,3-Dimethylol-5,5-dimethylhydantoin provide an enhancedreduction in bacterial numbers. (FIG. 2).

Example 3—Composition Based on Formulated THPS, Such as TOLCIDE® PS50Aand TOLCIDE® 4FRAC (Solvay), and 1,3-Dimethylol-5,5-Dimethylhydantoin,Such as DANTOGARD® 2000 (Lonza), Against General Heterotrophic BacteriaPseudomonas aeruginosa Contained in an Artificial Biofilm

Sample Preparation.

250 ppm 1,3-Dimethylol-5,5-dimethylhydantoin and 50 ppm formulated THPSwere used to treat an artificial biofilm containing GeneralHeterotrophic Bacteria Pseudomonas aeruginosa. A sterile QST medium wasused for the studies. The bacterial challenge comes from the artificialbiofilm. Studs were prepared from a 16 hour Pseudomonas aeruginosaculture grown in the appropriate growth medium. A sterile filter paper(Whatman No. 2) was placed onto an agar plate. 1 ml of 16 hr old culturewas placed onto the surface and spread over the filter paper using asterile spreader. Using sterile forceps 5 sterile freeze drying rubberbungs with O rings was placed onto the filter paper. The plates wereincubated at 30° C. for approximately 5 days until the plate was coveredwith growth. The studs with biofilm were exposed to the biocidetreatment for various contact times from 0 to 336 hours.

Sample Analysis.

The efficiency of the biocide treatments was measured using a standardquantitative suspension test (QST) method and enumerated using a mostprobable number (MPN) method. A typical QST procedure is described asfollows: 90 ml of QST medium is dispensed into glass screw cap bottles(100 ml nominal capacity) with magnetic followers and cap with themodified tops. The bottles and contents were sterilised by autoclaving(121° C. for 15 minutes). On cooling a further 9 ml of sterile QSTmedium was added to the bottles to bring the final volume to 99 ml.Immediately prior to the test the biocide stock solutions(1,3-Dimethylol-5,5-dimethylhydantoin and THPS) were prepared in sterileQST medium at a concentration such that when 1.0 ml was added to thetest bottles the desired concentration was achieved (final test volume100 ml). They were added to the test samples immediately followingpreparation The bottles were placed on a Multiplate magnetic stirrer tomix the biocide. The stock solutions were prepared at concentrations ona weight for volume basis mg/ml such that when 1.0 ml was added to theinoculated QST medium (final volume 100 ml) the desired finalconcentration of biocide was achieved. Two bottles were set up perbiocide being tested per time point and two bottles for a biocide freecontrol. Using sterile forceps one stud was removed from the plate,taking care not to disturb the biofilm, and using the modified topsplace in the test bottles. Approximately 2 ml amounts of sterile glassbeads of 1.5 to 2.5 mm diameter and sterile acid washed sand 50-150 meshwas dispensed into sterile screw cap plastic universal containers (30 mlnominal capacity). To these was added 10 ml sterile neutralisingsolution, QST medium supplemented with 5 g/L Sodium Thiosulphate and 5g/L Glycine. One container is required per stud. A further two studs areremoved from the plates for the Time 0 control samples and placeddirectly into the neutralising medium. The contents were vortex mixed atmaximum speed in 3 consecutive 45 second bursts with a 15 secondinterval between each burst. The purpose of this procedure is tomechanically remove biofilm from the surface of the coupons and tofurther disrupt the removed biofilm into small fragments therebyproducing a reasonably uniform dispersion of biofilm for enumeration. Analiquot of 5 ml was removed from each bottle and pooled into a thirdbottle and mixed thoroughly. 1.0 ml aliquots were removed from thepooled dispersion mix and inoculated into the first tube of a dilutionseries. This was carried out in duplicate. A serial dilution (10 foldsteps) was carried out in the appropriate growth medium. At thepredetermined time points the studs were removed from the test samplesand place in the neutralising medium. The studs were processed in thesame way as for the control sample. 1 ml aliquots were inoculated forthe pooled samples in the first tube of a dilution series. This wascarried out in duplicate. A serial dilution (10 fold steps) was carriedout in the appropriate growth medium, with the first tube in each seriescontaining the same medium supplemented with glycine (5.0 g/l) andsodium thiosulphate (5.0 g/1) to inactivate any residual biocide carriedinto the dilution series with the QST medium. The dilution series wasincubated at 25° C. and read after 48 hours. The end point was scored asthe highest dilution in the series to show turbidity.

The experiment shows that the combination of formulated THPS and and1,3-Dimethylol-5,5-dimethylhydantoin provide an enhanced reduction inbacterial numbers after a 24 hour contact time. (FIG. 3).

Example 4—Co-Application of THPS and1,3-Dimethylol-5,5-Dimethylhydantoin, Such as DANTOGARD® 2000 (Lonza),Against Planktonic Sulphate Reducing Bacteria

Sample Preparation.

250 ppm and 500 ppm 1,3-Dimethylol-5,5-dimethylhydantoin and 50 ppm THPSwere used to treat a planktonic sulphate reducing bacterial culture. Forthe marine strains used the basal medium used is Artificial Sea Water(ASW) (ASTM D1141-90). Inocula of mixed SRB population was prepared bygrowth in a modified Postgate's Medium C. Cultures were grown inPostgate's Medium C for between 48 to 64 hours at 30° C. (18 ml volumescontained in 20 ml capacity crimp cap serum vials with rubber septa.)The Basal medium (approximately 270 ml) was dispensed into 300 mlnominal capacity medical flats with screw cap and sterilised byautoclaving at 121° C. for 15 minutes. On cooling 10 ml of growthsupplements was added to the basal medium and the medium innoculatedwith the mixed SRB population (18 ml). The medical flats were incubatedat 30° C. for 72 hours until the medium had developed significantturbidity and the dissolved sulphide concentration was in excess of 100mg/l.

Sample Analysis.

The efficiency of the biocide treatments was measured using a standardquantitative suspension test (QST) method and enumerated using a mostprobable number (MPN) method. The QST procedure is described as follows:At the start of the QST 18 ml volumes of culture were dispensed intopre-sterilised 20 ml capacity crimp cap serum vials with rubber septa.Two serum vials were used for each biocide in the test and the biocidefree control. For those serum vials containing biocide one of the pairis used to sample at 45 and 90 minutes and the other at other relevanttime points. Fresh stock solutions of biocide in Artificial Sea Waterare prepared to ASTM D1141-91 and added to the QST medium immediatelyfollowing preparation. The stock solutions were prepared atconcentrations on a weight for volume basis mg/ml such that when 0.5 mlof the stock solution was added to the test sample (final volume 18.5ml) the desired final concentration of biocide is achieved. 0.50 ml ofsterile ASW was added to the biocide free controls instead of thebiocide stock solution. The samples were mixed thoroughly and placed inan incubator (30° C.) for the duration of the test. Controls weresampled throughout the experiment. For each sample point a separateserum vial was used. At each sample point 2×1.0 ml aliquots was removedfrom the serum vials using a 1.0 ml syringe and 21 gauge needle this wasused to inoculate the first vial of a duplicate dilution series inPostgate's Medium B. A dilution series was carried out and incubated at30° C. The series was read at intervals of up to 4 weeks. The end pointwas scored as the highest dilution in the series to show iron sulphideprecipitation (blackening).

The experiment shows that the combination of formulated THPS and and1,3-Dimethylol-5,5-dimethylhydantoin provide an enhanced reduction inbacterial numbers after a 4 hour and 24 hour contact time.

Example 5—End-Use Formulations of THPS and1,3-Dimethylol-5,5-Dimethylhydantoin, Such as DANTOGARD® 2000 (Lonza),Formulation Stability, Performance Against Planktonic GeneralHeterotrophic Bacteria Pseudomonas aeruginosa and Lactobacillus brevis

Table 1 illustrates that stable formulations were observed after fourmonths storage at room temperature and 50° C.

TABLE 1 THPS:1,3- Formaldehyde % THPS assay Value after 4 StorageDimethylol-5,5- (HCHO) % w/w month's storage. Temp dimethylhydantoin at4 months 0 1 2 4 Room Temp 1:1.25 <0.2% w/w 19.82 19.41 19.35 19.42 50°C. 1:1.25 <0.2% w/w — 19.41 19.00 18.06

Results in FIGS. 5 and 6 indicate a faster speed of kill versusPseudomonas aeruginosa especially at early time points for the end-useformulations. In Lactobacillus brevis experiments, the reduction ofbacteria to give a total kill is achieved at a 5 hour contact time.Performance of the THPS/1,3-Dimethylol-5,5-dimethylhydantoin formulationis 2 log orders better than THPS alone, such an improved performance atshort contact times is quite unexpected.

We claim:
 1. A method for preparing a well treatment fluid compositioncomprising the steps of: obtaining a composition comprising atetrakis(hydroxyorgano)phosphonium salt,1,3-dimethylol-5,5-dimethylhydantoin, and optionally one or more membersselected from the group consisting of: oxidizing viscosity breakers,quaternary ammonium compounds, and polymers of an unsaturated carboxylicacid or copolymers of an unsaturated carboxylic add with a sulphonicacid, said polymers or copolymers being terminated by a mono- ordi-phosphonated unsaturated carboxylic add group or having such monomersincorporated into the polymer backbone, wherein the composition achievesa reduction of bacteria to give a total kill at 5 hour contact time; anddiluting the composition to form a diluted composition.
 2. The method ofclaim 1, wherein the tetrakis(hydroxyorgano)phosphonium salt is selectedfrom the group consisting of tetrakis(hydroxymethyl)phosphoniumsulphate, tetrakis(hydroxymethyl)phosphonium chloride,tetrakis(hydroxymethyl)phosphonium phosphate,tetrakis(hydroxymethyl)phosphonium nitrate, andtetrakis(hydroxymethyl)phosphonium oxalate.
 3. The method of claim 1,wherein the composition includes an oxidizing viscosity breaker and thebreaker is selected from the group consisting of hydrogen peroxide,sodium persulfate, encapsulated ammonium persulfate, and sodiumchlorite.
 4. The method of claim 1, wherein the mass ratio between theTHP salt and 1,3-dimethylol-5,5-dimethylhydantoin is about 1:0.5 toabout 1:25.
 5. The method of claim 4 further including comprising atleast one oxidizing viscosity breaker.
 6. The method of claim 1, whereinthe composition contains less than 0.2% free formaldehyde after 4 monthsstorage at 50° C.
 7. The method of claim 4, wherein the compositioncontains less than 0.2% free formaldehyde after 4 months storage at 50°C.
 8. A method for treating a subterranean formation comprising the stepof introducing a composition into the formation, wherein the compositioncomprises a tetrakis(hydroxyorgano)phosphonium salt,1,3-dimethylol-5,5-dimethylhydantoin, and optionally one or more membersselected from the group consisting of: oxidizing viscosity breakers,quaternary ammonium compounds, and polymers of an unsaturated carboxylicacid or copolymers of an unsaturated carboxylic add with a sulphonicacid, said polymers or copolymers being terminated by a mono- ordi-phosphonated unsaturated carboxylic add group or having such monomersincorporated into the polymer backbone, wherein the composition achievesa reduction of bacteria to give a total kill at 5 hour contact time. 9.The method of claim 8, wherein the tetrakis(hydroxyorgano)phosphoniumsalt is selected from the group consisting oftetrakis(hydroxymethyl)phosphonium sulphate,tetrakis(hydroxymethyl)phosphonium chloride,tetrakis(hydroxymethyl)phosphonium phosphate,tetrakis(hydroxymethyl)phosphonium nitrate, andtetrakis(hydroxymethyl)phosphonium oxalate.
 10. The method of claim 8,wherein the composition includes an oxidizing viscosity breaker and thebreaker is selected from the group consisting of hydrogen peroxide,sodium persulfate, encapsulated ammonium persulfate, and sodiumchlorite.
 11. The method of claim 8, wherein the mass ratio between theTHP salt and 1,3-dimethylol-5,5-dimethylhydantoin is about 1:0.5 toabout 1:25.
 12. The method of claim 11 further including comprising atleast one oxidizing viscosity breaker.
 13. The method of claim 8,wherein the composition contains less than 0.2% free formaldehyde after4 months storage at 50° C.
 14. The method of claim 11, wherein thecomposition contains less than 0.2% free formaldehyde after 4 monthsstorage at 50° C.